v0.6.0

Bug-fix and stability release: crash fixes, a CI/lint pass, and a bad merge that had silently reverted two shipped features got corrected.

Fixed

• Two GTK segfaults in the remove/dependency confirmation dialogs, caused by mutating a widget after it was destroyed inside the same callback.
• A crash when installing or removing certain packages.
• Bundled symbolic icons never actually resolving via the hicolor fallback path.
• Transaction preview falsely reporting an error on exact-version-pinned reverse dependencies.
• Sidebar icon-rail (minimal) mode could corrupt its own state and leave stale styling after switching sidebar modes.
• caerus-helper now locks repository-config writes and validates ALTERNATIVE/VKPURGE arguments, closing a race/injection edge case.
• Several panics on unexpected GTK downcast failures hardened into graceful fallbacks instead of unwrap().
• A squashed merge had reverted the CSS-extraction commit and silently dropped the "close dialogs automatically on success" setting; both are restored.

Changed

• CI now runs clippy, fmt, and both build feature sets (plain / adwaita) on every push, plus a dependency-audit workflow.